How do you replace them? As for drilling them out the should be easy this is how i would remove all rivits mental as well.

The new/unused rivets push in to the holes and they have a long mandrel (?) protruding from the head. You gently tap it in with a mallet or some kind of hammer until it is flush with the head. I works kind of like a wall anchor with the sides of the rivet spreading out inside the rail as the mandrel is pushed in.